Photographic process



Jan. 3, 1967 R. W. YOUNG PHOTOGRAPHIC PROCESS Filed Dec.

INVENTOR.

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ATTORNEYS United States Patent Office 3,295,971 Patented Jan. 3, 1967 3,295,971 PHOTOGRAPHIC PROCESS Richard W. Young, Wellesley Hills, Mass., assignor to Polaroid Corporation, Cambridge, Mass., 2 corporation of Delaware Filed Dec. 4, 1962, Ser. No. 242,217 6 Claims. (Cl. 9629) This application relates to photography and, more particularly, to the treatment of sheet materials containing a photographic image subsequent to formation of said image.

In one aspect, the present invention is directed to a novel method for separating a first sheet material carrying a visible image from a second sheet material in superposed relationship thereto, said separation being subsequent to formation of said visible image by applying a processing solution between said two sheet materials.

In another aspect, the present invention is directed to a novel method for inhibiting color changes which may occur when a first sheet material carrying a color image is separated from a second sheet material held in superposed relationship thereto during processing to form said color image.

One object of the invention, therefore, is to provide a novel method for separating a first sheet material carrying a visible image from a second sheet material after processing to form said visible image.

Another object is to provide a novel method for separating a first sheet material carrying a visible image formed by diffusion transfer from a second sheet material comprising a photosensitive element held in superposed relationship thereto during processing.

Yet another object is to effect said separation by introducing a gas under pressure between said two sheet materials.

Still another object is to provide a novel method for inhibiting undesired color changes in col-or transfer images resulting when said color transfer image is separated from the photosensitive element subsequent to processing.

A still further object is to prevent or minimize said color change by introducing an acidifying gas between said color transfer image and said photosensitive element prior to separating said color image from said photosensitive element.

Other objects of the invention will in part be obvious and will in part appear hereinafter.

The invention accordingly comprises the process involving the several steps and the relation and order of one or more of such steps with respect to each of the others which are exemplified in the following detailed disclosure, and the scope of the application of which will be indicated in the claims.

For a fuller understanding of the nature and objects of the invention, reference should be had to the following detailed description taken in connection with the accompanying drawing wherein:

The figure is a perspective view showing the practice of this invention as applied to photographic prints obtained by using conventional self-developing cameras.

It is well known in the art to develop an exposed photosensitive element by applying a developing composition between the photosensitive element and a second sheet material. One procedure is to apply a monobath processing composition between the exposed photosensitive element and a second sheet material to form a negative image. However, the most common usage relates to diffusion transfer processes wherein an exposed photosensitive emulsion, e.g., a silver halide emulsion, is processed by spreading a developing composition between the exposed emulsion and a superposed image-receiving layer to form, by imbibition, a transfer image which may be a positive or negative image of the original subject matter, depending upon the particular system employed. Most commonly, the transfer image is a reverse or positive image of the original subject matter. Regardless of the system employed, the processing solution may initially be confined in a frangible container and processing effected by rupturing the container and spreading of its contents substantially uniformly between the photosensitive emulsion and the image-receiving layer. Processes of this nature are disclosed, for example, in US. Patents Nos. 2,543,181 and 2,634,886, both issued to Edwin H. Land. Transfer processes, such as disclosed in the aforementioned patents, utilizing roll film units are especially useful in commercially available self-developing Polaroid Land Cameras, sold by Polaroid Corporation, Cambridge 39, Massachusetts. Such cameras are disclosed, for example, in US. Patent No. 2,455,111.

In order to illustrate the present invention, its applicability to transfer images obtained by using self-developing cameras of the foregoing description will be described in detail, It will be appreciated, however, that the invention is not limited thereto, but has broad application in all photographic processes wherein processing to form the visible image is effected by spreading a processing or developing solution between two sheet materials.

In the well-known self-developing Polaroid Land Cameras commercially available on the market, use is made of a roll film assembly comprising a roll of negative film containing a plurality of frames having a layer or stratum of a light-sensitive emulsion, e.g., a silver halide emulsion; and a roll of sheet material containing an image-receiving layer and having afiixed thereto at spaced intervals, a plurality of frangible containers confining aviscous processing composition.

In operation, a frame of the negative film is photoexposed and the thus exposed frame is subsequently advanced in superposed relationship with the roll of sheet material containing the image-receiving layer and at least one frangible container. Further advancement of the now superposed film assembly through a pair of pressure rollers causes rupturing of the frangible container and spreading of the viscous processing composition between the superposed elements, thus developing the exposed emulsion and forming, by imbibition, a positive transfer image of the original subject matter. The camera is provided with a hinged door which may be opened to reveal the developed film assembly. Preferably, the sheet material containing the transfer image is provided with perforations or score lines to facilitate detachment and removal of the finished print from the remainder of the film assembly, in which case removal is customarily effected by fracturing a portion of the score lines with ones fingernail and then gripping and tearing the print along the remainder of the score lines.

While the use of ones fingernail to initiate separation of the completed print is completely satisfactory for most users of the self-developing cameras of the foregoing description, it will be appreciated that there are users who, for one physical reason or another, find this method of separation awkward and sometimes even difiicult to perform.

One aspect of the present invention, as was indicated heretofore, is directed to a novel method of separation which facilitates separation of the finished print.

It has now been found that separation of the completed print from the remainder of the film assembly can be simply and efiiciently performed by introducing a quantity of gas under pressure between the print and the adjacent surface of the remainder of the film assembly.

The introduction of gas under pressure has the further advantage of insuring complete separation of the finished print from the residue of the processing composition. Ideally, the finished print should be completely separated, none of this residue remaining after separation. Nevertheless, there is a tendency for minor amounts of the residual processing composition to adhere to the print. It has now been found that this tendency for adherence is appreciably minimized by the present invention, thus insuring complete separation of the finished print.

The particular apparatus employed for introducing the gas is not critical and devices for storing and dispensing gas under pressure which may be used in the practice of this invention are well known to those skilled in the art. For example, cartridges containing carbon dioxide and intended primarily for the preparation of carbonated beverages are well known and commercially avail-able. Also useful in the practice of this invention are the spray can type of dispensers now commonly employed in the packaging and dispensing art. The gas may be stored in the dispenser in other than its gaseous state, where found desirable or expedient to do so. For example, many spray-type dispensers commercially employed utilize nitrous oxide or similar gases under sufficient pressure to maintain the normally gaseous material in its liquid form.

The particular gas employed in the practice of this embodiment of the invention is not critical, although it will be appreciated that use is preferably made of a gas which is nontoxic and has no adverse effect upon the quality of the print. As an example of useful gases, mention may be made of air, inert gases such as nitrogen, carbon dioxide, halogenated hydrocarbons, etc., and mixtures containing such gases.

The use of a gas under pressure to separate a sheet material containing a visible image from a second sheet material in superposed relationship thereto will be more readily apparent by reference to the accompanying drawing which illustrates the practice of this invention, as applied to positive prints formed by utilization of the selfdeveloping cameras of the foregoing description.

As shown in the drawing, door' 11 of a typical selfdeveloping Polaroid Land Camera has been opened subsequent to development to reveal print 12 in superposed relationship with the photosensitive element (not shown) from which it was prepared. Print 12 is provided with score lines 12a to facilitate separation of the print. A conventional spray-type container or dispenser 13 is gripped in the hand of the practitioner and nozzle 14 of container 13 is inserted between print 12 and the photosensitive element. In conventional fashion, release means 15 is compressed, as by applying pressure with the thumb, to effect discharge of gas from container 13 via nozzle 14. The internal pressure created by the discharged gas causes print 12 to be separated at least in part from the photosensitive element, thus providing suificient gripping means to facilitate complete separation of the finished print.

In addition to providing a novel means for separation, the practice of this invention is particularly useful in the treatment of monochromatic or multicolor images formed by diffusion transfer processes wherein an aqueous alkaline processing solution is employed to effect transfer, by imbibition, of color image-forming constituents to an image-receiving element to form the color image. As an example of such processes, mention may be made of diffusion transfer processes utilizing dye developers, e.g., compounds which are both a dye and a silver halide developing agent, such as are described and claimed in U.S. Patent No. 2,983,606, issued to Howard G. Rogers.

It has been found that in transfer processes of this nature there may be a tendency for undesired color changes, such as the so-called greying, to result immediately upon separation of the print and exposure to air. Al though the exact chemical reaction resulting in the unwanted color change is not clear, it is known that this change is produed by a chemical reaction which takes place in the presence of air. It has also been found that the reaction which results in a change in the spectral absorption characteristics of a finished color print is facilitated by the rather high alkalinity, generally a pH of 10 or more, of the processing solution contacting the print. This high alkalinity produces a pH environment conducive to reaction, in the presence of air, of compounds transferred tothe image-receiving element, and the undesired color change is a product of this reaction.

It has now been found that the color change problem may be materially minimized if not completely obviated by introducing an acidifying gas between the finished color print and the remainder of the film assembly prior to separation and exposure of the print to air. The acidifying gas may be introduced in the manner previously described and illustrated in the drawing. The volume of gas introduced may or may not be sufficient to effect separation, although in the preferred embodiment the volume of gas introduced is sufiicient to perform the dual function of both inhibiting color change and effecting separation of the color print. In any event, the volume of acidifying gas introduced is preferably sufiicient to reduce materially the alkalinity in the environment of the finished print. It will be appreciated, however, that introduction of even a relatively small amount of gas will reduce the alkalinity at least to some extent and is therefore beneficial. It will also be appreciated that the volume of gas necessary to obtain a particular desired degree of imbibition will in part be dependent upon its acidity or ability to neutralize the alkaline environment and will be in part dependent upon the pH or amount of alkaline material to be neutralized. In other words, the amount of gas necessary to produce a given result will be in part dependent upon the particular gas employed and will be in part dependent upon the alkalinity of the particular processing solution employed to obtain the transfer image.

As used herein and in the appended claims, the term acidifying gas connotes a gas or mixture of gases capable of materially reducing the alkalinity of the environment of the finished print. While various useful acidifying gases or mixtures containing at least one acidifying gas and useful in practicing this aspect of the invention will be readily apparent to those skilled in the art, particularly satisfactory results have been obtained with carbon dioxide, a safe, commercially available and relatively inexpensive gas.

The following examples show by way of illustration and not by way of limitation the practice of the aforementioned embodiments of the invention.

Example 1 A commercially available film assembly including a photosensitive element containing a high speed gelatino silver halide emulsion, an image-receiving element containing a silver receptive stratum and a frangible container confining a processing solution comprising an aqueous alkaline solution of a silver halide developer and a silver halide solvent (such as described in the aforementioned US. Patents Nos. 2,543,181 and 2,634,886) was exposed and developed in one of the commercially available Polaroid Land Cameras (such as described in the aforementioned US. Patent No. 2,455,111). After development was completed, the door of the portion of the camera housing the developed film assembly was opened and the nozzle of a gas cartridge similar to that shown in the figure and containing carbon dioxide under pressure was gently forced between the finished print and the remainder of the film assembly. The release valve was actuated until enough gas was introduced to raise the print from the remainder of the film assembly and fracture a portion of the score lines, thereby permitting sufficient gripping area to facilitate complete separation of the finished print.

Example 2 A multicolor film assembly, such as described in the aforementioned U.S. Patent No. 2,983,606 and including a multilayer photosensitive element comprising a bluesensitive silver halide emulsion and an associated yellow dye developer; a green-sensitive silver halide emulsion and an associated magenta dye developer; and a red-sensitive silver halide emulsion and an associated cyan dye developer, was photoexposed and processed in a commercially available Polaroid Land Camera to form a multicolor dye image by diffusion transfer. Upon separation of the finished print and subsequent exposure to air, a greying was immediately observed. Although the picture was sharp and clear, had good detail and contrast, and was in all respects aesthetically pleasing, a greying of the flesh tones and of areas containing appreciable amounts of cyan dye was noticeable.

Example 3 The film assembly of Example 2 was exposed and developed in the identical manner described in the example. However, before exposure to air, carbon dioxide gas was introduced in the manner described in Example 1. Upon complete separation of the finished print, it was observed that the flesh tones appeared quite natural, the color balance appeared to be shifted to the warmer side, and the color reproduction of the finished print more closely approximated the color of the subject matter than did the print prepared in Example 2. The quality and other characteristics of the print were substantially similar to the print prepared in Example 2, the only noticeable difference between the two prints being the aforementioned color differences.

It will be apparent from the foregoing description and illustrative examples that the present invention in one aspect provides a simple and efiicient means for separating a sheet material containing a visible image from a second sheet material in superposed relationship thereto. It will also be apparent that another aspect of the present in vention provides a novel method for inhibiting color changes which may occur when the first sheet material containing a color image is separated from a second sheet material held in superposed relationship thereto during the processing to form said color image.

Since certain changes may be made in the above process without departing from the scope of the invention herein involved, it is intended that all matter contained in the above description or shown in the accompanying drawing shall be interpreted as illustrative and not in a limiting sense.

What is claimed is:

1. In a process of forming an image in color by diffusion transfer including the steps of spreading an aqueous alkaline processing composition between an exposed lightsensitive stratum and a superposed image-receiving layer, forming an imagewise distribution of color image-providing constituents and transferring said constituents, by imbibition, to said image-receiving layer to form a color image thereon, the improvement which comprises introducing an acidifying gas between said image-receiving layer containing said color image and said stratum prior to separating said layer from said stratum and exposing said image to air.

2. In a process of forming an image in color by spreading an aqueous alkaline processing composition between an exposed photosensitive element comprising at least one light-sensitive silver halide emulsion and a superposed image-receiving layer, forming an imagewise distribution of color imageproviding constituents comprising at least one compound that is both a dye and a silver halide developing agent, and transferring said constituents, by imbibition, to said image-receiving layer to form a transfer dye image thereon, the improvement which comprises introducing an acidifying gas between said layer containing said dye image and said photosensitive element prior to separating said layer from said element and exposing said separated dye image to air.

3. A process as defined in claim 2 wherein said image is a multicolor dye image.

4. A process as defined in claim 2 wherein the quantity of gas introduced between said layer and said stratum is sutficient to reduce materially the pH of said alkaline processing solution.

5. A process as defined in claim 2 wherein the quantity of gas introduced is sufficient to cause at least partial separation of said layer containing said dye image from said photosensitive element.

6. A process as defined in claim 2 wherein said gas comprises carbon dioxide.

References Cited by the. Examiner UNITED STATES PATENTS 2,337,724 12/1943 Mackie 271-26 2,441,912 5/1948 Streich 271-26 2,454,762 11/ 1948 Belluche 27126 3,158,481 11/1964 Shanefield 96-29 NORMAN G. TORCHIN, Primary Examiner.

I. TRAVIS BROWN, Assistant Examiner. 

1. IN A PROCESS OF FORMING AN IMAGE IN COLOR BY DIFFUSION TRANSFER INCLUDING THE STEPS OF SPREADING AN AQUEOUS ALKALINE PROCESSING COMPOSITION BETWEEN AN EXPOSED LIGHTSENSITIVE STRATUM AND SUPERPOSED IMAGE-RECEIVING LAYER, FORMING AN IMAGEWISE DISTRIBUTION OF COLOR IMAGE-PROVIDING CONSTITUENTS AND TRANSFERRING SAID CONSTITUENTS, BY IMBIBITION, TO SAID IMAGE-RECEIVING LAYER TO FORM A COLOR IMAGE THEREON, THE IMPROVEMENT WHICH COMPRISES INTRODUCING AN ACIDIFYING GAS BETWEEN SAID IMAGE-RECEIVING LALYER CONTAINING SAID COLOR IMAGE AND SAID STRATUM PRIOR TO SEPARATING SAID LAYER FROM SAID STRATUM AND EXPOSING SAID IMAGE TO AIR. 